The present invention relates to a rotor blade for a centrifugal compressor with a medium flow coefficient.
More precisely, the invention relates to a cylindrical blade for a centrifugal rotor of a multi-stage compressor.
In the field of centrifugal compressors, the flow coefficient is defined as "PHgr"=(4*q)/(xcfx80*d2*uxe2x80x3) in which:
q is the volume flow rate;
d is the outer diameter of the rotor;
uxe2x80x3 is the peripheral velocity of the rotor.
This dimensionless coefficient can be used to define the operating characteristic of the compressor, and can be used to classify the different types of compressor at the design stage.
Compressors are therefore made to handle different flow rates, in other words to operate with different values of the flow coefficient, according to the applications for which they are intended.
For example, we may mention compressors with a medium flow coefficient, in which has values in the vicinity of 0.04, and compressors with a medium-high flow coefficient, for which "PHgr" is approximately 0.06.
However, one of the main requirements common to all compressors relates to the high aerodynamic efficiency which must be attained in most of the stages.
The geometric configuration of the rotor blading significantly affects the aerodynamic efficiency, due to the fact that the geometric characteristics of the blade determine the distribution of the relative velocities of the fluid along the rotor, thus affecting the distribution of the boundary layers along the walls and, in the final analysis, the friction losses.
The aerodynamic efficiency is particularly critical for rotors made with stages having two-dimensional blades, in other words purely radial rotors in which the blades are flat or cylindrical with generatrices parallel to the axis of rotation of the rotor.
Conventionally, for reasons of economy in manufacture, the blades used in this type of rotor have a relatively simple geometry in which the median line of the section consists of an arc of a circumference and the thickness is constant along the blade, except in the region of the leading edge, which is formed by a semicircular fillet or, in particular cases, by a tapering of the thickness.
Although two-dimensional blades are made by relatively simple machining processes and are therefore very widely used, their geometry does not enable a high aerodynamic efficiency of the rotor to be achieved.
A first object of the present invention is therefore to provide a blade which, by means of a suitable configuration, enables a high aerodynamic efficiency to be achieved.
Another object of the present invention is to provide a blade which can be manufactured economically on a large scale by automated processes.
These and other objects of the present invention are achieved with the rotor blade for a centrifugal compressor with a medium flow coefficient according to the content of claim 1.
Further characteristics of the blade according to the invention are described in the subsequent claims.